King Arthur, king of kings Book

The early chapters give a fair summing up of early Arthurian literature, and of cross-pollination between Romantic, Celtic and Welsh literature (one way or the other - Avalon = Annwn, etc). A first pricking of my thumb, however, when it does identify Guinevere as Gwenhyfar, but fails to see that the name has the same origin as Ganhumara.
The further you go in the book, the more assumption is built on speculation, supported by guesswork, and it becomes a fragile structure indeed.
The truth about King Arthur is: if you strip away everything from the legend that we don't know, we remain only with the fact that there once was a warlord called Arthur. Maybe.